1. Field of the Invention
The present invention relates to a display apparatus, and in particular to a display apparatus using a liquid crystal display and a method for driving the liquid crystal display. More specifically, the invention relates to a display apparatus using a liquid crystal display containing liquid crystal and resin as well as a method for driving this liquid crystal display.
2. Description of the Related Art
As proposed in U.S. Pat. No. 4,688,900, liquid crystal display having particular liquid crystal and resin does not require a polarizer and preparation of a cell, and therefore it has been expected to apply it to a liquid crystal panel having a large area and a high brightness.
U.S. Pat. No. 5,437,811 has disclosed that a liquid crystal display, which comprises chiral nematic liquid crystal having a positive dielectric anisotropy and resin of 10% by weight with respect to a total weight, exhibits a bistability of a transparent state and an opaque state between the voltage-on and voltage-off conditions.
Further, U.S. Pat. No. 5,251,048 has disclosed a display apparatus, which uses a liquid crystal display proposed in the foregoing U.S. Pat. No. 5,437,811, and performs display by a-line-at-a-time matrix driving.
Thus, in this display apparatus, a liquid crystal display is retained between two transparent plates. A plurality of parallel scanning line paths are arranged on an inner side of one of the transparent plates, and a plurality of parallel segment line paths perpendicular to the scanning line paths are arranged on an inner side of the other transparent plate. In the liquid crystal display retained between the transparent plates, therefore, a potential difference corresponding to a difference between a voltage applied to the scanning line path and a voltage applied to the segment line path occurs at a point (picture element) where the scanning line path and the segment line path cross each other. In this manner, a transmissive state and an opaque state are selected at each picture element. More specifically, a particular voltage is applied to a selected scanning line path. This voltage can cooperate with a voltage applied to the segment line paths crossing the selected scanning line path, and thereby can set each of the picture elements on the selected scanning line path to a transmissive state or a scattering (opaque) state. All the scanning line paths other than the above are supplied with another voltage, which cooperates with a voltage applied to the segment line paths crossing these scanning line paths and thereby does not change the state of corresponding picture elements on the scanning line paths. This selection of the scanning line path is successively repeated, whereby the whole screen can be redrawn.
In the display apparatus disclosed in U.S. Pat. No. 5,251,048, however, a long time is required for changing the state of each picture element on the selected scanning line path, and more specifically, a time of about 100 msec is generally required for change the state of each picture element from a transmissive state to a stable scattering state and vice versa. Therefore, if a speed of selection of the scanning line path is increased, a new scanning line path is selected before picture elements on a last selected scanning line path attain a stable state, so that the picture elements on the last selected scanning line path attain neither a transmissive state nor a scattering state, and are stabilized in a state intermediate these states. Thus, rapid driving of this display apparatus is difficult.
Further, in this display apparatus, each picture element cannot be stabilized at an intended intermediate state, so that it is difficult to display an image with multiple gradation.
It is an object of the invention to provide a display apparatus using a liquid crystal display and allowing rapid driving as well as a method for driving the display apparatus allowing rapid driving and particularly the liquid crystal display of the same.
It is also an object of the invention to provide a display apparatus capable of displaying an image with multiple gradation by a liquid crystal display as well as a method for driving the display apparatus capable of displaying an image with multiple gradation and in particular the liquid crystal display of the same.
In order to achieve the above objects, the present invention provides display apparatuses of the following first, second and third types.
First Type: A display apparatus including a liquid crystal display having a pair of plates with electrodes and a liquid crystal layer retained between the plates, and a driver connected to the liquid crystal display to apply voltage pulses to the electrodes, the driver applying a first voltage pulse for changing a state of the liquid crystal layer and after a predetermined lapse of time further applying a second voltage pulse to set the liquid crystal layer to a stable state.
Second Type: A display apparatus including a liquid crystal display having a pair of plates with electrodes and a liquid crystal layer retained between the plates, a driver connected to the liquid crystal display for applying a first voltage pulse and a second voltage pulse following the first voltage pulse, and a controller connected to the driver to adjust a width of the second voltage pulse in accordance with desired gradation.
Third Type: A display apparatus including a liquid crystal display having a pair of plates with electrodes and a liquid crystal layer retained between the plates, a driver connected to the liquid crystal display for applying a first voltage pulse and a plurality of second voltage pulses following the first voltage pulse, and a controller connected to the driver to adjust levels of the second voltage pulses in accordance with desired gradation.
In order to achieve the above objects, the present invention provides the following method for driving a liquid crystal display.
A method for driving a liquid crystal display having a pair of plates with electrodes and a liquid crystal layer retained between the plates, including the steps of applying a first voltage pulse to the electrodes of the liquid crystal display to change a state of the liquid crystal layer, and applying, upon elapsing of a predetermined time after application of the first voltage pulse, a second voltage pulse to the electrodes to set the liquid crystal layer to a stable state.
According to the display apparatuses of the first, second and third types as well as the method for driving the liquid crystal display of the invention, which have been described above, one or more of magnitudes, pulse widths and pulse intervals of the first and second voltage pulses may be appropriately determined, whereby the optical state of the liquid crystal can be set to an intended state, i.e., a transmissive state, a scattering state or an intermediate state, so that the image with multiple gradation can be displayed.
A time required for stabilizing the liquid crystal at an intended optical state can be shorter than that in the conventional method in which the optical state of the liquid crystal is selected by applying only one time a voltage pulse, and the two states, i.e., transmissive and scattering states of the liquid crystal can be selected only by a slight change in magnitude and/or width of the second voltage pulse. Therefore, a scanning speed can be increased, so that rapid driving is allowed. Furthermore, the voltage applied to picture elements on unselected scanning line paths can be small.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention and the accompanying drawings.